Page 404 - Feline Cardiology

426 Section P: Cardiac Screening Programs

all of the individuals with a causative mutation will actu- Use of an animal with a congenital defect for breeding
ally show the trait and they will not all show the same should be strongly discouraged. Although an animal
disease severity. For example, some Maine coon cats with with a defect does not necessarily suggest a heritable
the Maine coon hypertrophic cardiomyopathy mutation trait, there is a risk of passing on even a spontaneously
may have severe ventricular hypertrophy and develop occurring trait to the progeny. Additionally, queens with
congestive heart failure; littermates with the same muta- congenital heart disease may be personally put at risk
tion may not ever show the disease. The mechanisms for with the fluid shifts and stress of pregnancy.
the phenomenon of variable disease penetrance are Repeated use of an unaffected animal that has pro-
poorly understood even in human genetics. It is possible duced a single or even litters of affected kittens is not
that environmental or genetic factors may have an necessarily wrong since the defect may or may not be
impact on a particular mutation. Importantly, not all heritable. However, since it is possible that an unaffected
individuals that carry a genetic mutation or are the off- animal could carry a recessive heritable trait, it should
spring of affected parents will show the disease, or will not be bred to the same mate again since it is possible
show it with the same severity. that they both carry a recessive trait. The breeder can be
advised to breed again with a different mate. Additionally,
CONGENITAL DEFECTS they should not breed to a related mate (also called line
Overall, the incidence of congenital heart defects in the breeding), because this could emphasize a recessive trait
cat is much less common than the incidence of acquired as well. If additional affected offspring are produced, the
heart diseases like cardiomyopathies (see Section D). individual cat should no longer be used for breeding.
Although many congenital defects have been demon- Adult Onset Disease
strated to be inherited in the dog, this has not yet been
shown in the cat and the majority of congenital heart Hypertrophic cardiomyopathy is the most common
defects do not appear to be overrepresented in a particu- heart disease for which cardiac screening is requested
lar breed. because it is the most common adult onset cardiac
disease in the cat and a familial etiology has been dem-
Diagnosis onstrated in at least some breeds (Kittleson et al. 1999;
Congenital defects in cats are most commonly charac- Meurs et al. 2005, 2007). Although there is some evi-
terized by a significant structural change in the heart dence that there is a familial component to development
that results in turbulent blood flow, so the presence of a of DCM with taurine deficiency, it is not typically
heart murmur should be the first indication of the screened for since taurine supplementation can cause
underlying defect. However, presence of an arrhythmia resolution of the disease (Pion et al. 1987; Lawler et al.
is also abnormal in kittens, and may also suggest a con- 1993).
genital heart defect. Careful echocardiographic evalua-
tion, ideally by a veterinary cardiologist, should be HYPERTROPHIC CARDIOMYOPATHY
performed to accurately diagnose the type of defect.
This is important for planning of a breeding program, Signalment
since not all defects will be inherited in the same way Hypertrophic cardiomyopathy has been demonstrated
and knowledge of the defect will help in making accu- to be inherited in the Maine coon and Ragdoll breeds
rate recommendations. However, a specific mode of (Kittleson et al. 1999; Meurs et al. 2005, 2007). It has
genetic transmission for any feline congenital defect is been suggested that it may be inherited in other breeds
not known. as well including Sphynx, British shorthair, Norwegian
Screening Recommendations studies have not been done. In the Maine coon, hyper-
Forest cat and Siberian among others, but complete
Very little is known about the inheritance of congenital
trophic cardiomyopathy has been demonstrated to be
defects in the cat and very few breed predispositions inherited as an autosomal dominant trait (Meurs et al.
have been observed (see Chapter 10). The lack of infor- 2005). Hypertrophic cardiomyopathy is likely to be
mation about the heritability of specific defects means inherited in the same mode in the Ragdoll as well, but
that strong recommendations usually cannot be pro- definitive proof is lacking at present.
vided. It should also be remembered that not all defects
are heritable; some are simply spontaneously occurring. Diagnosis
The infrequent identification of a congenital heart defect The antemortem diagnosis of hypertrophic cardiomy-
in a breeder’s line should not result in significant concern opathy is based on echocardiography (see Chapter 7).
about an inheritable trait. Screening programs classify cats as clear, indeterminate,